Information on the most widely used ASTM standards within the materials testing industry
Fatigue testing simulates the cyclic loading that tibial trays endure during long - term clinical use, which is the core part of the standard.
| Parameter | Specification | Rationale |
|---|---|---|
| Loading Waveform | Sinusoidal waveform | Simulates the periodic mechanical load of the knee joint during daily activities |
| Load Ratio (R) | 0.1 (minimum load = 10% of maximum load) | Maintains a stable compressive baseline to avoid damage caused by alternating tension - compression loads |
| Test Frequency | 5 - 10 Hz | Balances test efficiency and simulation accuracy, avoiding material heating due to excessive frequency |
| Cycle Count Requirement | 10 million cycles (minimum) | Equivalent to 2 - 3 years of moderate activity for an average patient, covering the short - to medium - term service life of the implant |
| Peak Load | Determined by the static test results, usually 30% - 50% of the ultimate static load | Ensures the test load is close to the actual physiological load level |
Test Termination: The test stops when the specimen fractures, visible cracks appear, or the preset 10 million cycles are completed.
Acceptance and Fixtures
| Fixture Component | Function | Design Requirements |
|---|---|---|
| Tibial Tray Fixing Block | Fix the tibial tray to simulate in - vivo implantation | Made of high - rigidity alloy steel, with a groove matching the keel of the tibial tray to ensure precise positioning |
| Load Applicator | Apply static or cyclic load to the tray | Equipped with a spherical pressure head (covered with UHMWPE pads) to avoid local stress concentration and simulate the contact state between the femoral component and the tibial tray |
| Displacement and Force Measuring System | Collect real - time load and displacement data | The force sensor accuracy is not less than ±1% of the full - scale range, and the displacement measurement resolution is not less than 0.001 mm |
| Environmental Simulation Device (Optional) | Simulate the in - vivo physiological environment | A constant - temperature water bath at 37°C ±2°C can be used to replicate the temperature and humidity of the human body |
| Aspect | ISO 14879 - 1 | ASTM F1800 |
|---|---|---|
| Applicability | Global universal, adopted by most countries and regions | Mainly used in the North American market |
| Test Cycle | Minimum 10 million cycles | Minimum 10 million cycles (consistent with ISO) |
| Loading Frequency | 5 - 10 Hz | 0.5 - 10 Hz (wider range) |
| Fixture Design | More detailed requirements for the simulation of in - vivo fixation (such as bone cement usage) | Focuses on the simplicity and repeatability of the fixture |
| Scope of Application | Only for metallic tibial trays | Covers metallic tibial trays of fixed - bearing knee systems |
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